Electronically controlled steering system

Abstract

A power steering gear mechanism for vehicles with a variable assist characteristic having primary and secondary steering valve portions, the primary portion controlling pressure in a power steering fluid motor, a steering control valve that controls the magnitude of the steering assist as a function of vehicle speed the secondary steering valve portion developing a steering torque signal, and an electronic signal processor for controlling the steering control valve in response to changes in the vehicle speed and the steering torque signal.

Having described a preferred form of my invention, what I claim and desire to secure by U.S. Letters Patent is: 
     
       1. A power steering gear system for controlling the dirigible wheels of a vehicle comprising: a constant flow fluid pressure pump;   a gear mechanism having a torque input member adapted to receive driver steering torque and a torque output member adapted to be connected to the dirigible wheels and a fluid motor having a pressure movable member for augmenting steering torque;   a steering valve assembly having primary and secondary valve portions with registering valve lands that define variable fluid flow areas, and primary valve lands controlling pressure distribution to opposite sides of said pressure movable member to provide a pressure steering assist;   a high pressure passage connecting the flow inlet side of said primary valve portion with the high pressure side of said pump and a low pressure passage connecting the flow outlet side of said primary valve portion with the low pressure side of said pump;   a steering assist control solenoid valve means communicating with said high pressure passage and said low pressure passage for establishing a bypass flow between said high pressure passage and said low pressure passage;   a steering torque pressure passage extending from said high pressure passage to the inlet side of said secondary valve portion;   a steering torque sensor flow control valve means disposed in and forming a part of said steering torque pressure passage for establishing a constant flow to said secondary valve portion;   an electronic processor unit including a data input portion, an output driver portion and a memory portion, said driver portion being connected to said solenoid valve, said memory portion having stored therein desired functional relationships between steering torque and steering pressure for various vehicle speeds; and   a steering torque pressure sensor and a vehicle speed sensor connected to the data input portion of said processor unit, said pressure sensor being connected to said steering torque pressure passage.   
     
     
       2. The combination as set forth in claim 1 wherein said steering assist control valve means comprises a flow area control having a valve chamber, a multiple land valve spool in said valve chamber, valve ports registering with said valve lands, one port communicating with the high pressure side of said pump and the other port communicating with the other side of said pump, means for urging said spool in one direction to open communication between said ports and a solenoid actuator urging said spool in the opposite direction whereby the flow area of the bypass flow across said pump is controlled. 
     
     
       3. The combination as set forth in claim 2 wherein said solenoid actuator received a pulse time controlled voltage signal from said processor unit whereby said spool tends to move between a bypass open position and a bypass closed position, the amount of bypass flow across said pump is determined by the average pulse time for a given time interval.